What is an annular fissure at L5?

What is an Annular Fissure at L5?

An annular fissure at L5 is a tear or defect in the annulus fibrosus (the tough outer ring of the intervertebral disc between L5 and the sacrum), which appears as a hyperintense signal on T2-weighted MRI and represents a structural weakness that may or may not be the source of low back pain.

Structural Definition and Types

An annular fissure is a disruption in the layered collagen fibers that comprise the annulus fibrosus of the intervertebral disc. 1 These defects are classified into three main types:

• Peripheral tears: More frequent in the anterior annulus (except at L5-S1 where they occur posteriorly), typically caused by trauma rather than biochemical degradation 1
• Circumferential tears: Equally distributed between anterior and posterior annulus 1
• Radiating tears: Almost exclusively located in the posterior annulus and closely associated with severe nuclear degeneration 1

MRI Appearance and Characteristics

The imaging hallmark of an annular fissure is hyperintensity on T2-weighted MRI sequences, representing fluid or granulation tissue within the tear. 2, 3

Key imaging features include:

• T2 hyperintensity persists over time: In 88% of cases, the high signal remains visible on follow-up imaging (mean 21.9 months), making it impossible to determine acuity based on signal intensity alone 3
• Contrast enhancement: When present (28-70% of cases), enhancement typically persists on follow-up studies, again providing no reliable indicator of acute versus chronic injury 3, 4
• High-intensity zone (HIZ): A specific type of annular fissure appearance that may indicate increased risk for future disc extrusion through the weakened annular tissue 5

Clinical Significance and Limitations

The presence of an annular fissure on imaging does NOT reliably correlate with symptoms or predict clinical outcomes. 2

Critical clinical considerations:

• Common in asymptomatic individuals: Annular fissures are frequently found in people without back pain, with prevalence increasing with age [2, @12@]
• No correlation between tear location and pain side: Studies show random correlation between the side of a concordantly painful annular tear and the side of patient's pain 6
• Uncertain relationship to low back pain: The association between peripheral annular lesions and low back pain remains unclear, though they may play a role in discogenic pain pathogenesis 1
• Imaging findings remain stable: Repeat imaging in patients with new LBP episodes who have previous MRI scans are unlikely to detect differences in annular fissures 2

Natural History

Annular fissures demonstrate remarkable stability over time:

• Rarely resolve: Once present, annular fissures typically persist on serial imaging 3, 4
• Signal characteristics remain: T2 hyperintensity persists in the vast majority of cases, though intensity may decrease in approximately 24% 3, 4
• Disc herniation risk: Annular fissures, particularly those manifesting as HIZ, may represent sites of structural weakness predisposing to future disc extrusion 5

Management Implications

The presence of an annular fissure at L5 should NOT drive treatment decisions in isolation. 2

Management principles:

• Imaging is not indicated for acute uncomplicated low back pain: Even when annular fissures are present, they do not change initial conservative management 2
• Conservative treatment remains first-line: At least 6 weeks of conservative therapy (physical therapy, activity modification, pain management) should be attempted regardless of annular fissure presence 7, 8
• Clinical correlation is essential: Treatment decisions must be based on clinical presentation, not imaging findings alone 2, 8

Common Pitfalls to Avoid

• Over-interpreting imaging findings: Annular fissures are common incidental findings that may not be the pain source 2, 8
• Premature imaging: Early imaging without red flags leads to increased healthcare utilization and unnecessary interventions 2
• Assuming acuity based on MRI appearance: Neither T2 hyperintensity nor contrast enhancement can determine whether an annular fissure is acute or chronic 3, 4
• Focusing on imaging rather than clinical presentation: This leads to inappropriate treatment decisions 2, 8